Flame stabilizer for burner for flame hydrolysus deposition

ABSTRACT

A flame stabilizing apparatus is disclosed for application to a burner for a flame hydrolysis deposition (FHD) process. In the flame stabilizing apparatus, a co-flow diffusion flame burner emits a flame onto a substrate and a flame stabilizer, installed around the burner coaxially, isolates the emitted flame from an instable ambient flow to stabilize the flame and a particle flow.

CLAIM OF PRIORITY

[0001] This application claims priority to an application entitled“Flame Stabilizer for Burner for Flame Hydrolysis Deposition” filed inthe Korean Industrial Property Office on Jul. 21, 2001 and assignedSerial No. 2001-44004, the contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a fine particlefabricating burner using flame hydrolysis deposition (FHD), and inparticular, to a flame stabilizer for a burner to stably form a thinfilm with fine particles to be used as a light waveguide on a wafer byflame.

[0004] 2. Description of the Related Art

[0005] In general, FHD is a technology developed from fiber preformtechniques and modified to produce planar waveguide geometry. A vapormixture of halides (SiCl4, GeCl4, etc) is reacted in an oxy-hydrogenflame to form fine glass particles, which are deposited directly onto asuitable substrate, e.g., silicon. The high-silica technology offers thepotential of integrating a number of passive functions on a siliconchip, as well as the possibility of hybrid integration of both activeand passive devices onto a silicon motherboard.

[0006] Flame-using fine particle formation is performed byoxygen-hydrogen flames generated from a co-flow diffusion flame burnerhaving a plurality of concentric nozzles. Being fed with flames, asource material forms fine particles by means of flame hydrolysis oroxidation. The fine particles migrate with the flames, grown bycollision-caused coagulation, and adhere to a substrate in various formsby thermophoresis. The fine particles then are sintered and driedaccording to their use, for example, by OVD (Outside Vapor Deposition)or VAD (Vapor-phase Axial Deposition) in fabricating an optical fiber,and FHD in fabricating a planar optical waveguide thin film.

[0007] Planar optical waveguide technology has added the growth of theInternet and multimedia communications. These areas are also driving thedemand for more and more capacity on networks, and the medium of choicefor high-bandwidth is optical fiber. There are three technologies toincrease the overall data rate in an optical link: space divisionmultiplexing (SDM) using multiple fibers in parallel, time divisionmultiplexing (TDM), i.e. higher bit rate per channel and fiber, andwavelength division multiplexing (WDM), i.e., more channels per fiber bymaking use of different wavelengths for the transport of data.

[0008] Long-haul backbone networks already use all three strategies toexploit the enormous bandwidth of the optical fiber. Transmission ratesin the Terabit per second (Tb/s) range over more than 100 WDM channelshave been demonstrated in laboratories around the world.

[0009] Planar optical waveguide technology, for example, enablesfunctions such as adding and filtering out specific wavelengths to beperformed efficiently and flexibly at low cost.

[0010]FIGS. 1 and 2 are schematic views of a co-flow diffusion flameburner 100 having a plurality of concentric nozzles for use in theconventional FHD process. The term ‘diffusion flame’ can imply that thefuel and oxidizer (air) gas streams mix together in a chemical reactionzone by mass diffusion.

[0011] Referring to FIGS. 1 and 2, a flame F is generated by sprayingsource materials and a carrier gas from the center of the co-flowdiffusion flame burner 100 in a direction A, with combustion of hydrogen(H₂) and oxygen (O₂) outside the center, respectively in directions Band C. The source materials for forming particles usually include SiCl₄,GeCl₄, and POCl₃. Since these materials are liquid at room temperature,they are used after bubbling by the carrier gas. Hydrolysis occurs whereH₂O or OH resulting from the combustion of H₂ and O₂ meets the sourcematerials diffused from the center of the burner 100. The resultingparticles migrate with the flame F and stick to a silicon wafer W bythermophoresis.

[0012] The particles generated and grown in the flame F are as small asseveral nanometers to tens of nanometers. For particles this small, theinfluence of inertia can be neglected. The velocity of the particles inthe flame F is the sum of the velocity of the gas and a thermophoreticvelocity over a temperature gradient.

[0013] Therefore, in the case where the flow of the flame F is a laminarflow that can define a streamline, the particles in the flame F show asimilar velocity distribution. On the other hand, if the flame flow is aturbulent flow with velocity fluctuation that cannot define astreamline, the particles in the flame F move at an unstable velocityalong with the flow. As a result, the deposition efficiency anddeposition uniformity of the particles is reduced.

[0014] The co-flow diffusion flame F generated from the burner 100 isgenerally unstable for two reasons. First, a shear flow is formed due tothe velocity difference between the gases sprayed from the concentricnozzles and determined by process conditions, that is, formation of theflame F, source materials, and the flow rate of the carrier gas. Thesecond reason is that entrainment of an ambient gas and a shear flowcaused by the velocity and pressure differences between the flame F andthe ambient gas. The entrainment of the ambient gas and the shear flowdepend on the flow outside the flame F.

[0015] In the general FHD process, the flame F attracted by gravitationis positioned by rotation or linear movement over the silicon wafer Whaving a relative velocity in a direction D with respect to the burner100. An exhaust flow is absorbed in a direction E into a discharge tube12 for discharging non-deposited particles. The flame F exists in thevicinity of the flame F. A natural convection phenomenon is observed dueto heating of the silicon wafer W and the flame F itself is influencedby buoyancy in a direction G. Hence, the flame F and the flow around theflame F are vulnerable to instability.

[0016] A flame shield tube 10 is usually provided to the periphery ofthe co-flow diffusion flame burner 100 to prevent introduction ofambient air and thus stabilize the flame F.

[0017] However, this method is not effective in fundamentally overcomingthe instability of the flame F formed after passing through the flameshield tube 10. Therefore, high particle deposition efficiency anduniformity cannot be expected. Moreover, a vortex arising from anunstable flow causes contamination by allowing glass soot particles thatare not deposited on the silicon wafer W to stick to the outside of theburner 100 or inside a deposition chamber. For at least these reasons,an improved burner design is needed

SUMMARY OF THE INVENTION

[0018] It is, therefore, an object of the present invention to providean improved flame burner.

[0019] It is another object of the present invention to provide a flamestabilizer for a burner, which stabilizes a flow around a co-flowdiffusion flame to prevent the disturbance of the flame and a particleflow in the flame caused by the ambient flow with increased particledeposition efficiency and stable and uniform particle deposition.

[0020] It is another object of the present invention to provide a flamestabilizer for a burner, which prevents the burner and a depositionchamber from being contaminated with glass soot due to a vortex and aflow disturbance around a flame.

[0021] The foregoing and other objects of the present invention areachieved by providing a flame stabilizing apparatus for application to aburner for an FHD process. In the flame stabilizing apparatus, a co-flowdiffusion flame burner emits a flame onto a substrate and a flamestabilizer, installed around the burner coaxially, isolates the emittedflame from an instable ambient flow to stabilize the flame and aparticle flow.

[0022] Another aspect of the present invention relates to a method forstabilizing a flame from an instable ambient flow and particle flow. Themethod includes the steps of inserting source materials into a center ofa co-flow diffusion flame burner and inserting an inert gas that is notinvolved in flame hydrolysis through a plurality of channels juxtaposedto the center of the burner. The method also includes the step ofallowing the insert gas to develop into a flow in the same direction asan emitted flame.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0024]FIG. 1 is a schematic view of a conventional burner for FHD,illustrating formation of a thin film on a silicon wafer by spraying aflame from the burner;

[0025]FIG. 2 is a frontal view of the burner shown in FIG. 1;

[0026]FIG. 3 is a sectional view of a burner with a flame stabilizeraccording to a preferred embodiment of the present invention; and

[0027]FIG. 4 is a schematic view of the burner with the flame stabilizeraccording to the preferred embodiment of the present invention,illustrating formation of a thin film on a silicon wafer by feeding aflame from the burner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] In the following description, for purposes of explanation ratherthan limitation, specific details are set forth such as the particulararchitecture, interfaces, techniques, etc., in order to provide athorough understanding of the present invention. For purposes ofsimplicity and clarity, detailed descriptions of well-known devices,circuits, and methods are omitted so as not to obscure the descriptionof the present invention with unnecessary detail.

[0029]FIG. 3 is a sectional view of a burner with a flame stabilizeraccording to a preferred embodiment of the present invention.

[0030]FIG. 4 is a schematic view of the burner with the flamestabilizer, illustrating formation of a thin film on a silicon wafer byspraying a flame from the burner.

[0031] Referring to FIGS. 3 and 4, a flame stabilizing apparatusincludes the co-flow diffusion flame burner 100 and a flame stabilizer30 for the burner 100. Source materials and a carrier gas for bubblingthe source materials are sprayed from the center of the burner 100 inthe direction A. The flame F is generated by combustion of a mixture ofhydrogen and a diluting gas for temperature control in the direction B.As a oxidizer, oxygen flows in the direction C outside the center.Additionally, a flame shield tube 10 (see FIG. 4) is provided to preventthe introduction of air around the burner 100 and thus to stabilize theflame F.

[0032] The source materials for forming particles usually include SiCl₄,GeCl₄, POCl₃, and BCl₃.

[0033] The flame stabilizing apparatus according to one embodiment ofthe present invention includes the co-flow diffusion flame burner 100and the flame stabilizer 30 around the burner 100. The flame stabilizer30 sprays a gas to stabilize the flame F against an ambient flow. Theflame stabilizer 30 is hollow and substantially surrounds the burner 100coaxially. However, it should be noted that other configurations mayalso used as long as they are juxtaposed to the center of the co-flowdiffusion flame burner 100. For example, the flame stabilizer 30 neednot completely surround the burner 100. Also, the outer shape of theflame stabilizer 30 may vary.

[0034] More specifically, the flame stabilizer 30 is composed of aplurality of preferably ceramic honeycomb tubes 32, which are stacked inthe outer circumferential direction. Other configurations for the flamestabilizer 30 may also be used, e.g. a plurality of channels ormulti-branching passages. In addition, other flame retardant and/orresistant materials may be used other than ceramic. The diameter of theplurality of tubes 32 need not be the same at both ends. It is alsonoted that a plurality of cross-sectional shapes can be used for thehoneycomb tubes, e.g., circular, square, oval, hexagon, etc. The tubes32 may be arranged in a random pattern or stacked in a grid-like arraypattern.

[0035] In operation, the flame stabilizer 30 sprays inert gases (seeFIG. 4) that are not involved in flame hydrolysis, such as O₂, N₂, Ar,He, etc. through the ceramic honeycomb tubes 32. Passing through thesmall diameter (relative to the diameter of the flame shield tube 10)honeycomb tubes 32, the inert gases becomes filly developed flow. Then,the fully developed inert gases have only a velocity component in thesame direction as that in which the flame F is emitted at the outlet ofthe flame stabilizer 30.

[0036] This arrangement causes a velocity component perpendicular to theflame emitting direction to be removed from the fully developed inertgases. If the inert gases are directed in multiple layers in a directionH around the flame F, the flows in the direction perpendicular to theflame emitting direction, caused by the introduction of stationary air,can be blocked or minimized. Also, the instability of the flame F due toa shear flow and a suction flow caused by the relative velocitydifference in the direction D between the silicon wafer W and the burner100 can be minimized.

[0037] In particular, spraying, forcing or inserting the inert gasesaround the flame F from the co-flow diffusion flame burner 100 throughthe multi-layered honeycomb tubes 32 prevents the flame F from theinstability caused by the natural convection and the suction flow. Itshould be understood by one of ordinary skill in the art that the burner100 with the flame stabilizer 30 shown in FIG. 4 is a sectional view inflame F emitting direction, and the stabilizer 30 surrounds the burner100 coaxially.

[0038] As described above, in application to a co-flow diffusion flameburner for FHD, the inventive flame stabilizing apparatus uses a flamestabilizer for spraying inert gases with a velocity in the flameemitting direction in multiple layers around a flame. This has theeffect of removing instability caused by factors other than the flameand thus maintaining the flame and a particle flow in the flame at thestate of a laminar flow. Consequently, the thermophoresis effect withrespect to a temperature gradient is maximized and the particle massdeposited on a silicon wafer and particle deposition uniformity areincreased when source materials of the same mass are used. Furthermore,suppression of flow disturbance around the flame prevents contaminationof the FHD burner and a deposition chamber with glass soot. Theresulting obviation of periodical cleansing of the burner preventsdamages to the burner and reproducibility deterioration.

[0039] While the invention has been shown and described with referenceto a certain preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A flame stabilizing apparatus comprising: aco-flow diffusion flame burner for emitting a flame onto a substrate ina flame hydrolysis deposition (FHD) process; and a flame stabilizerjuxtaposed to the burner for isolating the emitted flame from aninstable ambient flow to stabilize the flame and a particle flow.
 2. Theflame stabilizing apparatus of claim 1, wherein the flame stabilizer ispositioned around the burner coaxially.
 3. The flame stabilizingapparatus of claim 2, wherein the flame stabilizer includes a pluralityof channels and emits a gas in a fully developed flow around the flamethrough the channels.
 4. The flame stabilizing apparatus of claim 3,wherein the channels are honeycomb tubes.
 5. The flame stabilizingapparatus of claim 4, wherein the honeycomb tubes are stacked in atleast one layer along the outer circumferential direction.
 6. The flamestabilizing apparatus of claim 1, wherein the flame stabilizer is formedof ceramic.
 7. The flame stabilizing apparatus of claim 1, wherein theflame stabilizer sprays an inert gas.
 8. The flame stabilizing apparatusof claim 1, wherein the inert gas includes oxygen, nitrogen, argon, andhelium.
 9. The flame stabilizing apparatus of claim 1, wherein the flamestabilizer surrounds the outer circumference of the burner and sprays agas in the same direction as that in which the flame is emitted.
 10. Aflame stabilizing apparatus comprising: a co-flow diffusion flame burnerfor emitting a flame onto a substrate in a flame hydrolysis deposition(FHD) process; and flame stabilizer means for isolating the emittedflame from an instable ambient flow to stabilize the flame and aparticle flow.
 11. A method for stabilizing a flame from an instableambient flow and particle flow, said method comprising the steps of:inserting source materials into a center of a co-flow diffusion flameburner; inserting an inert gas that is not involved in flame hydrolysisthrough a plurality of channels juxtaposed to the center of the burner;and allowing the insert gas to develop into a flow in the same directionas an emitted flame.